1. Field of the Invention
This invention relates to an oil flooded rotary compressor, and more particularly, to an oil flooded rotary compressor which includes a fire extinguishing apparatus for controlling internal fires in oil flooded rotary compressors.
2. Description Of The Prior Art
Oil flooded rotary screw and vane compressors are well known in industries utilizing compressors. They are more efficient, quieter, and easier to maintain than piston type compressors. These benefits come with the considerable risk of a large volume of combustible lubricating oil which is used to provide three necessary functions, namely; lubrication, sealing, and cooling.
The lubrication function is applied to bearings, shafts, and gears. The oil is also used to provide sealing between the rotors and the housings in which they run. Lubrication, sealing, and especially compression of the air create a large amount of heat which raises the temperature of the oil. The compressed air and oil are discharged into the oil reservoir which usually also serves as the air receiver.
After being separated from the air, the hot oil is piped to a heat exchanger where the oil is cooled so that it can be reused safely. Thus the oil is used for it's critical third function as a heat exchange fluid.
Rotary compressors are efficient and reliable machines, but they have a bad fire record. It should be recognized that fires occur when a suitable fuel, air, and ignition source are present at the same time. These compressors, working with normal air, have a flow of air and a large amount of combustible lubricant, all heated to a fairly high temperature. All that is needed is an ignition source or a high enough temperature to start a fire.
Attempts have been made to adapt fire suppression apparatus to compressors to control fires. Heretofore, virtually all suppression apparatus use a dry chemical extinguishing agent. These apparatus have failed on actual internal fires as the agent was applied externally while the fires were inside the compressors.
An internal fire within a compressor will cause a severe rise of both temperature and pressure. In tests reported in the literature, where oil flow was purposely stopped or delayed in the compressor, maximum temperatures as high as 600 to 800 degrees C. and pressures up to 15.8 bar g were measured. Since safety (relief) valves generally are set at about 3 bar above the operating pressure, the internal fire is vented generally through the safety valve; but, it may also be vented through other discharge vents or ports which typically may be associated with the control systems of the compressor. In the event of an internal fire, the air within the compressor will expel the products of combustion. Also it will generally expel an excess of oil as the amount of oil in the compressor is considerably greater than the amount of oxygen present to complete combustion of the oil so there may be much unburned oil in the discharge of the safety valve or other vents. Typically the release of the internal fire through the safety valve will spray hot gases and burning oil over a considerable area and at a distance from the compressor. In one very destructive fire, there is evidence that the discharged oil was burning 30 feet from the compressor and combustible material in the vicinity of the compressor had been ignited.
Automatic sprinkler or water spray systems, external to the compressors, have been proposed to protect against the possibility that an internal fire in a compressor could spread to external combustibles, such as a building or stored material. Because the release of gases and oil is intense, the application of the water would have to be quick and the rate should be very high. A particular consideration would be that the sprinkler or water spray system would have to cover a large area as the oil can be sprayed over a considerable distance. Since the discharge pattern of the burning oil from the safety valve is broad and unpredictable, the total water discharge rate might have to be quite large. These fire suppression systems, which must be connected to a water supply, do not lend themselves to portability. The erection of a large automatic sprinkler or water spray system would be a much greater job than setting up a compressor.
Dry chemical systems are not well adapted to controlling large area fires. The dry chemical agent does not cool and its discharge time is generally limited to 15 seconds or less. Since the discharge of gases and burning oil from the safety valve can be much longer, a dry chemical extinguishing system may have exhausted its agent before the discharge of burning oil stops. Water extinguishing systems cool, can cover large areas, and can discharge for long periods of time or until shut off. They are considered to be technically superior but usually are slower to react.
It should be noted that the external fire suppression systems discussed heretofore operate only after a sensing means has detected the presence of flame or an unusual temperature increase on the outside of the compressor. Detection systems require time to respond. Automatic sprinklers, which are regarded as exceptionally reliable, do not respond rapidly. None of these fire suppression systems can prevent the release of flame which, if combustible dust were present, might cause an explosion.
Other apparatus have been proposed that would detect the fire either by sensing internal pressure rise, internal temperature rise, or both. They would respond by releasing, internally within the compressor, a dry chemical agent, a gaseous agent such as halon, or an inerting agent, such as carbon dioxide. The very severe risk of this method is that the release of any agent internally would cause a large and rapid pressure rise in addition to the pressure and temperature rise already caused by the fire. This could overstress the air receiver, or some other component of the compressor, so that it might explode, resulting in a much more serious fire or loss of life.
U.S. Pat. No. 2,470,655 discloses the use of a water soluble oil mixed with water and applied internally to provide cooling and lubrication for compressors.
U.S. Pat. No. 2,523,317 discloses the use of compressed air as a cooling agent in rotor vanes that functions by expansion and cooling.
U.S. Pat. No. 2,701,634 discloses an oil circulating system for rotary compressors.
U.S. Pat. No. 2,983,435 discloses a flow system for lubricating fluid and a control apparatus for oil pumping systems.
U.S. Pat. No. 3,850,554 discloses a rotary compressor utilizing water internally as a cooling and sealing medium.
U.S. Pat. No. 4,025,244 discloses an apparatus for correlating the lubricating liquid volume with the volume of gas drawn into the rotary compressor.
U.S. Pat. No. 4,289,461 discloses a control valve controlled by temperature sensors at the air inlet and after the liquid separator that control the flow of liquid lubricant through a liquid cooler. This patent also discloses temperature sensors located at the air inlet and after the liquid separator to control a valve shunting water around the liquid cooler.
U.S. Pat. No. 4,526,523 discloses an oil pressure control system using a pneumatic control valve to bypass a quantity of the oil pump output in order to relieve the pump of excessive energy demands.
Although the prior art discloses cooling and fire extinguishing apparatus, there is a need for an improved fire control apparatus that is portable, inexpensive, does not increase the risk of explosion, and will prevent the release of flame, burning oil, or gas or oil hot enough to start external combustion.